USB 6008_Lab View Power Monitor

[johnsold]

Milinda,

You definitely should use transformers (PT and CT) for isolation as well as signal magnitude division.  Trying to connect the USB-6008 to a shunt resistor in an power circuit will likely result in a destroyed USB-6008, a destroyed computer, and possibly a destroyed Milinda!

The phase shift can be measured with either a resistive shunt or with a CT.  Because the CT is a transformer and thus has some reactance associated with it, you should do some calibration (or at least verification) measurements when you get the system put together.  Any commercial CT designed for power frequency measurements will probably have very low phase shift with a burden resistor.

!!!!  If you are not familiar with these concepts, I urge you to be very careful so that no one gets hurt!  Power line measurements can be dangerous!  !!!!!!

Your question about the Digital I/O port current makes me wonder how much you know about electricity and electrical measurements.  What kind of load did you use when attempting to measure the current available at the Digital Output?

Lynn

[Power Monitoring and control unit]

Thanks Lyyn for you warnings,

I’m using a shunt resistor to measure the voltage across it and give it as a differential voltage input to the DAQ. I'm not inputting a 230V line into the DAQ.

The safe way is to use a PT and a CT as you say.

I got a solution for the Digital I/O problem. It gives really small current, so I'm using that output to drive the base of a transistor and drive the LED connected in series with the Collector.

Cheers,

Milinda

[Clamphius]

Dear Milinda,

Can you please tell me which step down transformer did you use for this purpose?

Thank you very much in advance.